Method and apparatus for improving sheet formation of dissolving wood pulp



Ucit. 4, 1955 F. R. CHARLES J A METHOD AND APPARATUS FOR IMPROVING SHEETFORMATION OF DISSOLVING WOOD PULP Filed Feb, 18, 1952 2 Sheets-Sheet l 251 15? Dryew Secfzn; F5747 ryer Sec Z6072:

F. R. CHARLES 2,719,4'64

METHOD AND APPARATUS FOR IMPROVING SHEET FORMATION OF DISSOLVING WOODPULP 2 Sheets-Sheet 2 Filed Feb. 18, 1952 32 IN V EN TOR. 33' 3/? flan?/?Q?'Z 'S.

United States Patent Ofiice 2,719,464 Patented Oct. 4, 1955 METHOD ANDAPPARATUS FOR IMPROVING SHEET FORMATION OF DISSOLVING WOOD PULP Frank R.Charles, Hawkesbury, Ontario, Canada, assigncr to Canadian InternationalPaper Company, Montreal, Ontario, Canada, a corporation of QuebecApplication February 18, 1952, Serial No. 272,182

18 Claims. (CI. 92-39) This invention relates to new and usefulimprovements in forming sheets of dissolving pulp and particularly seeksto provide a novel method of and apparatus for so modifying the pulpsheet structure that improved steeping can be attained when the pulp isto undergo conversion into a cellulose derivative.

One of the first steps in converting sheet pulp into cellulosederivatives such as viscose or cellulose others is to subject thepre-cut sheet of pulp to the action of strong caustic soda in a steepingpress to form alkali cellulose. The uniformity of penetration of thecaustic is dependent upon several factors, including filling speed,density of the pulp sheets and degree of loading of the steeping press.The steeping efiiciency may be and generally is empirically measured bythe extent of brown spotting which has occurred in the treated sheets.Thus, if as generally practiced, the pulp sheets are placed verticallyin compartments of a steeping press and suthcient caustic soda of about18% strength is run in until the sheets are covered, then steeping isallowed to continue for the required time (generally between fifteenminutes and two hours) and then the liquor is drained off and the alkalicellulose sheets hydraulically pressed until their weight is about threetimes their original dry weight, each sheet may be graded as having, forinstance, zero, 12 /2%, 25%, 50% or 75% brown spots based on the areaaffected and averaged for the contents of the whole press.

Since the caustic must be able to contact the entirety of each pulpsheet and since the sheets swell to from three to seven times theiroriginal thickness it has been heretofore considered proper practice toload the steeping presses with not more than 5.5 sheets per inch ofcompartment space based on a sheet weight of 52 grams per square foot.Heretofore, if the loading were increased above this amount freeswelling of the cellulose became more and more restricted andpenetration of the caustic between the sheets became less and lessperfect, resulting in areas of imperfect mercerization, as evidencedfirst by surface wrinkling of the sheets, then by brown spots. These arebIOW11COl0I6d due to imperfect removal of hemicellulose; they containonly about NaOH instead of the usual 15-16% and react imperfectly withcarbon disulphide and etherifying reagents.

Through the practice of the present invention it has been found possibleto so improve the physical formation of the pulp sheets that greatlyimproved steeping will occur with so-called normal loading of thesteeping presses and the improvement in steeping is plainly evidencedeven when the steeping presses are over-crowded in comparison with thepractices which have been heretofore considered proper. In addition togaining improved steeping when the pulp sheets are subjected toconversion operations this invention also provides means by which it ispossible to secure the improved sheet formation without the necessity ofemploying extremely expensive anti-deflection press rolls.

It is therefore an object of this invention to provide a method andapparatus for so modifying the formation of pulp sheets that greatlyimproved steeping characteristics will accrue when the sheets aresubjected to steeping operations.

Another object of this invention is to provide apparatus by whichimproved formation of pulp sheets and subsequent steeping operations maybe achieved through the use on the nearly dried pulp on a conventionaldrying machine of press sections in which the nip pressure between thepress rolls does not exceed normal practice.

Another object of this invention is to provide consecutively employedpress rolls having cooperatively aligned landed surfaces for improvingthe formation of a nearly dry web of pulp passing therebetween.

Another object of this invention is to provide apparatus of thecharacter stated in which the rolls at one press section are employed todensify parallel areas of a pulp web passing therebetween, and the rollsof another press section are employed to density at least a portion ofthe remaining areas of the web whereby to render the sheeted pulp moresusceptible to uniform caustic penetration when placed in a steepingpress.

With these and other objects in view, the nature of which will be moreapparent, the invention will be more fully understood by reference tothe drawings, the accompanying detailed description and the appendedclaims.

In the drawings,

Fig. l is a schematic side elevation of the last drying sections of atypical pulp drying machine into which have been incorporated inaccordance with the present invention two pairs of special press rolls;

Fig. 2 is an enlarged fragmentary transverse section taken generallyalong line 2-2 of Fig. l and shows in detail the landed structure of theends of one pair of press rolls;

Fig. 3 is a view generally similar to Fig. 2 but shows the arrangementof press rolls in which only the upper roll is landed;

Fig. 4 is a view generally similar to Fig. 2 but shows an arrangement ofpress rolls at the first press for densifyingonly a portion of the web;

Fig. 5 is a view similar to Fig. 4 but shows the disposition of therolls at the second press in order to complete the densification of theWeb while leaving longitudinal ridges of unpressed pulp;

Fig. 6 is a transverse section of a portion of the pulp Web as itappears after having been subjected to pressing actions in which onlythe upper press rolls have been landed in the same manner as shown inFigs. 4 and 5; and

Figs. 7 and 8 are generally similar to Figs. 4 and 5, respectively, butillustrative a slight modification in the disposition of the lands inorder that the web may be uniformly compacted across its full width.

By reference to the drawings in detail it will be seen that Fig. 1schematically illustrates the dry end sections of a typical continuouslyoperating pulp drying machine comprised of a plurality of steam-heateddrying cylinders and including two pairs of special press rolls locatedwhere the moisture of the sheet has been reduced to between 19 and 37%.We have found this to be the range of moisture content, reached towardthe final section of the pulp drying machine, wherein the compression ofthe sheet is most readily effected. From the dryer section the web ispassed to either sheeting apparatus or reeling apparatus in preparationfor subsequent handling.

The principles of this invention may be effected by suitable variationsin the configurations of certain of the press rolls, and in Fig. 2 ofthe drawings, for instance, an enlarged fragmentary end portion of thefirst press section C is shown in which a top press roll 4 and a lowerpress roll 5 are disposed in cooperatively opposed relationship. Theupper press roll 4 is provided with a series of spaced lands 6 separatedby relatively Wide grooves 7, and the lower press roll is similarlyprovided with a plurality of spaced lands 8 separated by grooved areas9. In this particular embodiment of the invention the opposed lands ofthe press rolls serve to compress a partly-dry pulp sheet having amoisture content between 19 and 37% in such a manner that on its upperand lower surfaces spaced parallel grooves are formed within the areasof which the web is densely compacted, and between such grooves the webundergoes substantially no mechanical compacting.

If in the case of the above mentioned embodiment of the invention itwere to be assumed that the loading between the upper press roll 4 andthe lower press roll was that which would produce with plain rollsurfaces a web sufiiciently compact for normal steeping in the steepingpress during the rayon conversion operations, it will be appreciatedthat due to the landed formation of both press rolls the grooving of theweb will effect a greatly increased densification thereof by comparisonwith that which could be produced with smooth surface press rolls. Forexample, if the press rolls are so constructed as to have /2" wide landson 2" centers and the loading of the first press section C is on theorder of 400 lbs. per lineal inch of roll length, 1600 lbs. pressurewill be effected in the areas of the lands, and grooves in the webcompressed to an extremely high degree will result. The pulp web thenpasses to the second press section D in which the rolls thereof areungrooved where the rolls are subjected to the same pressure of 400 lbs.per lineal inch to give an effect on the remaining portion of the web of400 %=530 lbs. per lineal incha worthwhile gainsince the grooves, havingalready been compressed at 1600 lbs. per lineal inch, are not contactedby any portion of the roll faces at the second press section andconsequently do not absorb any of the line pressure in the niptherebetween.

Fig. 3 of the drawings illustrates a modification of the presentinvention slightly different from that shown in Fig. 2 in that the firstpress section C is provided with an upper roll 4a landed similarly tothe press roll 4 with lands 6a and intermediate relatively'wide grooves7a. In this case, however, the lower press roll 5a is perfectly smoothacross its full width in order to provide for groov- 'ting 'only on theupper surface of the continuously moving web which passes between therolls. The pulp sheet then passes to the second pair of press rolls D,both of rayon conversion activities without having to employ more thannormal line pressure in pounds per lineal inchacross the face of thepress. The grooves are on only one side of the sheet but are twice asdeep and thus afford the same cross-sectional area for causticpenetration.

In Figs. 4 and 5 of the drawings there is illustrated a furthermodification which maybe made to the rolls of the first and second presssections of the machine in order to effect the improved sheet formationscontemplated by this invention. In this modification the first presssection C is provided with an upper press roll 10 having a plurality ofrelatively wide lands 11 andintermediate grooves 12 and a lower pressroll 13 having lands 14 and grooves 15 disposed in opposition to thelandsand grooves 11 and 12 of the upper press roll. If, for instance,the-upper and lower press rolls 10 and 13 of the first press section Cwere to be provided with 1 /3 lands on 4" centers with the first landslocated at the left-hand end of each press roll, as viewed in .Fig. 4,the resultant formation of .the web G as it passesthrough the nipbetween thepress =rolls 10 and 13 is clearly indicated in section inFig. 4 and provides alternate relatively wide bars of highly compressedpulp and uncompressed pulp. 'In this modification the grooving operationhas only been partially completed at this stage, and the'web is passed"to the second press "section D "which is provided with an upper pressroll 16 having alternate lands 17 and grooves 18 and a lower press roll19 having lands 20 and grooves 21 disposed in opposition to the lands 17and grooves 18 of the upper press roll. Channeling also is provided inthe finally formed sheets of pulp through the use of the presentmodification of this invention because the lands of the rolls of thesecond press section D are slightly less in width than the grooves ofthe rolls of the first press section C and the lands and grooves of therolls of D are reversed with respect to their position in C in orderthat the finally compacted web G may assume the cross-sectional shape asseen particularly in Fig. 5 of the drawings in which each face of theweb is provided with a plurality of relatively narrow ridges ofunpressed pulp. In the present instance the ridges would be /s wide andspaced on 2" centers. These ridges when the pulp sheets are subjected tosteeping operations in the rayon converting processes will keep thesheets from suction contact with each other and permit free access ofthe steeping caustic to the central area of the sheets. Furthermore,these low density ridges initially swell more rapidly than the densifiedremainder as the caustic level rises, tending to facilitate further thepenetration of caustic to all parts.

Fig. 6 of the drawings illustrates a slight modification of theformation of the Web G that can be produced through the use of presssection roll configurations such as previously discussed in connectionwith Figs. 4 and 5 but having, however, the upper rolls only of thefirst and second press sections landed, the lower rolls being smooth.

A further modification consists in having the landed roll of the secondpress section correspond in position with the smooth roll of the firstpress section whereby a sheet is formed with grooves alternating withrespect to sheet face yet still separated by strips of unpressed pulp.

The principles of this invention for compacting the pulp web intovarious grooved or ridged formations can also be applied to theproduction of smooth finished pulp webs in which the pulp has been muchmore greatly compacted than could be obtained through the use of normalpress sections without the use of expensive anti-deflection rolls ofsuch a type as to be capable of imparting substantially higher nippressures on a pounds-per-lineal-inch basis.

Figs. 7 and 8 of the drawings illustrate the manner in which the firstand second press sections C and D can have their upper and lower pressrolls landed for this purpose. Typically, the first press section Cwould be provided with an upper press roll 22, being provided with lands23 and grooves 24 in which the lands might be, say, 4" in width andspaced on 8" centers. The bottom press roll 25 would be provided withlands 26 and grooves 27 disposed in opposition to the respective lands23 and grooves '24 of the upper press roll 22. In a manner similar tothat discussed above in connection with the modification illustrated inFigs. 4 and 5 of the drawings the lands of the upper and lower pressrolls are shown as located at the left end thereof as viewed in Fig. 7of the drawings. In this case also the partially grooved web afterleaving the first press section C will pass through the second presssection D provided with an upper press roll 28 having lands 29 andgrooves 30. The lower press roll 31 of the second press D will beprovided with lands 32 and grooves 33 disposed in opposition .to thelands and grooves 29 and 30 of the upper press roll 28. Thus in thesecond press section D the first lands from the .left hand end as viewedin Fig. 8 of the drawings will be spaced 4" in from the end, and in thismanner the firstand second press sections together are enabled tocompact the sheet of pulp to -a smooth, uniformly dense body having across section of the type indicated in Fig. 8 of the drawings. In thismodificationit will be apparent that if in each of the first and secondpress sections Cand D a line pressure of 300 pounds per lineal inch 'isused its effective'value in compacting the pulp will be equivalent to600 pounds employed by a single press .section. In this way the present"invention provides means for employing two relatively inexpensivepresses instead of a costly anti-deflection press of the type previouslyfound necessary to apply high nip pressures to a Web evenly across thewidth of the Webforming machine.

In addition to providing for more ready penetration of the causticduring steeping operations, densification of the sheets serves the addedfunction of mechanically expressing a considerable quantity of free airfrom the sheets and thus to enhance subsequent steeping operations.Densitication also reduces the swelling speed and contorting of thesheets during filling of the steeping press with caustic soda solution.The contorting has the effect of artificially increasing the packing ofthe sheets between the compartment plates, causing pressure areas whereimperfect penetration of caustic occurs.

The following example illustrates some of the benefits which may beobtained through practice of this invention and it should be noted thatthe conditions of steeping to which the pulp sheets were subjected inthe steeping press represent abnormal crowding together of the sheets bycomparison with the normal space previously mentioned. It will beremembered that normal steeping is generally effected with not more than55 sheets per inch of compartment space whereas in the below givenexample the press was loaded with 7.5 sheets per inch of compartmentspace. The particular grooving employed in this example was with /8"intensely pressed grooves on 3 centers, the sheets being placed in thesteeping press with the grooves vertical.

The value of the grooved sheets is markedly shown by comparing Sample Ato Sample D in which the percentage of brown spots was reduced from 4.3to 1.3. The improvement is also shown strikingly by the SteepingQuality, a figure derived empirically from observations on the degree ofdisorder of the steeped sheets and the time required for escape ofentrapped air from them; 100 represents perfect steeping.

When grooved pulp sheets produced in accordance with this invention aresubjected to steeping operations the grooves, of course, swell to thesame sheet thickness as the rest of the sheet, but as hereinbeforementioned, there is a time delay due to the slower swelling of thegrooves which enables full penetration of the caustic liquor to thecenter of the sheets. For instance, in connection with Sample D abovethe natural filling speed for the grooved areas of the sheets was 1.8"per minute and for the rest of the sheet 3.0" per minute. A fillingspeed of 7" a minute was actually used.

Thus it will be seen that the present invention provides apparatus andmethod for so physically improving the formation of continuously formedwebs of highly purified cellulose pulp that marked improvements in itssteeping qualities are readily apparent when out sheets of the pulp aresubjected to steeping operations, and such advantages are even apparentin the event of overcrowding of the steeping presses. This inventionfurther provides means by which abnormally dense compacting of parallelareas of a continuously moving web of pulp can be effected through theuse of ordinary drying machine presses without the necessity ofemploying costly anti-deflection rolls.

It is, of course, to be understood that various details of arrangementsand proportions of parts may be modified within the scope of theappended claims.

I claim:

1. Apparatus for physically modifying the crosssectional configurationof a continuously moving sheet of cellulose pulp to enhance itsreceptiveness to caustic soda solution during subsequent steepingoperations comprising, a press section for a pulp drying machineincluding upper and lower press rolls, one of said rolls being providedwith alternate lands and grooves across its full width, said lands beingeffective to form a series of spaced parallel grooves of greatlycompacted pulp in a web of pulp passing through said press section.

2. Apparatus for physically modifying the cross-sectional configurationof a continuously moving sheet of cellulose pulp to enhance itsreceptiveness to caustic soda solution during subsequent steepingoperations comprising, a press section for a pulp drying machine including upper and lower press rolls, one of said rolls being provided withalternate lands and grooves across its full width, the other of saidrolls being similarly provided with alternate lands and grooves disposedin alignment with the lands and grooves of said first-mentioned rollwhereby to form on each face of a web of pulp passing through said presssection a series of spaced parallel grooves of greatly compacted pulp.

3. Apparatus for physically modifying the cross-sec tional configurationof a continuously moving sheet of cellulose pulp to enhance itsreceptiveness to caustic soda solution during subsequent steepingoperations comprising, a first press section for a pulp drying machineincluding upper and lower press rolls, one of said rolls being providedwith alternate lands and grooves across its full width whereby to formon one face of a web of pulp passing through said press section a seriesof spaced parallel grooves of greatly compacted pulp, and a second presssection including upper and lower press rolls, the one of said rollscorresponding in position with the landed roll of said first presssection being provided with alternate lands and grooves disposed instaggered offset relationship with respect to those of the correspondingroll of said first press section whereby to form on the same face ofsaid web of pulp a series of spaced parallel grooves of greatlycompacted pulp offset with respect to those formed by said first presssection.

4. Apparatus in accordance with claim 3 in which the landed roll of thesecond press section is disposed in a position corresponding to that ofthe unlanded roll of the first press section whereby to form on thereverse side of the pulp sheet a series of spaced parallel grooves ofgreatly compacted pulp alternating with those formed by the first presssection and separated therefrom by strips of unpressed pulp.

5. Apparatus for physically modifying the cross-sectional configurationof a continuously moving sheet of cellulose pulp to enhance itsreceptiveness to caustic soda solution during subsequent steepingoperations comprising, a first press section for a pulp drying machineincluding upper and lower press rolls, one of said rolls being providedwith alternate lands and grooves across its full width, the other ofsaid rolls being similarly provided with alternate lands and groovesdisposed in alignment with the lands and grooves of said first-mentionedroll whereby to form on each face of a Web of pulp passing through saidpress section a series of spaced parallel grooves of greatly compactedpulp, and a second press section including upper and lower press rollsprovided with aligned lands and grooves, the lands of both rolls beingoffset to coincide with the grooves of the first press section and beingnarrower than said grooves whereby to form on each face of said sheet aseries of spaced parallel grooves of greatly compacted pulp alternatingwith those formed by the rolls of said first press section and separatedtherefrom by ridges of unpressed pulp.

6. Apparatus in accordance with claim 3 in which the widths of the landsand grooves of the several press rolls are substantially equal and theamount of staggering of the lands of the second press section issubstantially equal to the Width of a single land whereby to greatlycompact said web of pulp across its full Width.

7. Apparatus in accordance with claim 5 in which the widths of the landsand grooves of the several press rolls are substantially equal and theamount of staggering of the lands of the second press section issubstantially equal to the width of a single land whereby to greatlycompact said web of pulp across its full width.

8. In a method of preparing sheets of highly purified wood pulp forconversion into cellulose derivatives, the step of forming on a surfaceof a web of pulp a series of spaced parallel grooved areas of greatlycompacted pulp whereby to permit ready penetration of treating chemicalsto the central areas of pulp sheets cut therefrom when such sheets aresteeped in a steeping press.

9. The method of claim 8 in which the grooving is initiated while thepulp web is of from 19 to 37% moisture content.

10, The method of claim 8 in which the grooves of greatly compacted pulpare formed on both faces of the web and in which the grooving isinitiated while the pulp web is of from 19 to 37% moisture content.

11. The method of claim 8 in which the grooves of greatly compacted pulpare formed on both faces of the pulp web.

12. In a method of preparing sheets of highly purified wood pulp forconversion into cellulose derivatives, the steps of forming on a surfaceof a web of pulp a series of spaced parallel grooved areas of greatlycompacted pulp, and then forming a second series of spaced parallelgrooved areas of greatly compacted pulp alternating with the firstformed grooves and separated therefrom by ridges of unpressed pulpwhereby to permit ready penetration of treating chemicals to the centralareas of pulp sheets out therefrom when such sheets are steeped in asteeping press.

13. The method of claim 9 in which the grooves of greatly compacted pulpare formed on both faces of the pulp web.

14. The method of claim 9 in which the second set of formed groovesoccupy the spaces between the first formed set of grooves whereby toproduce a pulp web that has been greatly compacted across its entirewidth.

15. The method of claim 9 in which the grooves of greatly compacted pulpare formed on both faces of the pulp web and in which the second set offormed grooves occupy the spaces between the first formed set of grooveswhereby to produce a pulp web that has been greatly compacted across itsentire width.

Cir

16. In a method of preparing sheets of highly purified wood pulp forconversion into cellulose derivatives, the steps of forming on a surfaceof a web of pulp a series of spaced parallel grooved areas of greatlycompacted pulp, and then forming a second series of spaced parallelgrooved areas of greatly compacted pulp alternating with the firstformed grooves and separated therefrom by ridges of unpressed pulpwhereby to permit ready penetration of treating chemicals to the centralareas of pulp sheets cut therefrom when such sheets are steeped in asteeping press, the formation of said parallel grooved areas beinginitiated while the pulp web is of from 1-9 to 37% moisture.

17. The method of claim 16 in which the second set of formed groovesoccupy the spaces between the first formed set of grooves whereby toproduce a pulp web that has been greatly compacted across its entirewidth.

18. The method of claim 16 in which the grooves of greatly compactedpulp are formed on both faces of the pulp web and in which the secondset of formed grooves occupy the spaces between the first formed set ofgrooves whereby to produce a pulp web that has been greatly compactedacross its entire width.

References Cited in the file of this patent UNITED STATES PATENTS159,515 La Monte Feb. 9, 1875 320,614 Beale June 23, 1885 502,337Wheeler Aug. 1, 1893 951,954 Loebbecke Mar. 15, 1910 1,033,992 CraneJuly 30, 1912 1,196,912 Week Sept. 5, 1916 1,344,826 Sexton June 29,1920 1,776,536 Blanco et al. Sept. 23, 1930 1,884,366 Sutherland Oct. 25 1 932 1,929,008 Wells Oct. 3, 1933 1,941,783 Bahr Jan. 2, 19341,944,093 Maggart Jan. 16, 1934 2,015,416 Toohey Sept. 24, 19352,216,803 Benda Oct. 8, 1940 2,245,014 Sherman June 10, 1941 FOREIGNPATENTS 19,250 Great Britain of 1889

3. APPARATUS FOR PHYSICALLY MODIFYING THE CROSS-SECTIONAL CONFIGURATIONOF A CONTINUOUSLY MOVING SHEET OF CELLULOSE PULP TO ENHANCE ITSRECEPTIVENESS TO CAUSTIC SODA SOLUTION DURING SUBSEQUENT STEEPINGOPERATIONS COMPRISING, A FIRST PRESS SECTION FOR A PULP DRYING MACHINEINCLUDING UPPER AND LOWER PRESS ROLLS, ONE OF SAID ROLLS BEING PROVIDEDWITH ALTERNATE LANDS AND GROOVES ACROSS ITS FULL WIDTH WHEREBY TO FORMON ONE FACE OF A WEB OF PULP PASSING THROUGH SAID PRESS SECTION A SERIESOF SPACED PARALLEL GROOVES OF GREATLY COMPACTED PUOP, AND A SECOND PRESSSECTION INCLUDING UPPER AND LOWER PRESS ROLLS, THE ONE OF SAID ROLLSCORRESPONDING IN POSITION WITH THE LANDED ROLL OF SAID FIRST PRESSSECTION BEING PROVIDED WITH ALTERNATE LANDS AND GROOVES DISPOSEDINSTAGGERED OFFSET RELATIONSHIP WITH RESPECT TO THOSE OF THECORRESPONDING ROLL OF SAID FIRST PRESS SECTION WHEREBY TO FORM ON THESAME FACE OF SAID WEB OF PULP A SERIES OF SPACED PARALLEL GROOVES OFGREATLY COMPACTED PULP OFFSET WITH RESPECT TO THOSE FORMED BY SAID FIRSTPRESS SECTION.